1. Field of the Invention
The present invention relates particularly to a fixing apparatus which is usable in image forming apparatuses such as a copying apparatus and a printer apparatus in an electrophotographic system using a thermally melting developer and which fixes a developer to an output object.
2. Description of the Related Art
A fixing apparatus incorporated in an image forming apparatus using an electrophotographic process applies heat to a toner (developer) positioned on an output object, that is, a recording material to soften the toner, and applies pressure to the toner to fix the toner to the recording material. In recent years, induction heating has been broadly utilized as a heating system capable of reducing a time from when power supply is started until temperature reaches a fixable temperature at which the toner softens, that is, a heating time.
However, in the fixing apparatus using the induction heating, it is difficult to correctly detect the temperature of a heat roller (heating member) for fixing the toner to the recording material.
There have been many proposals in order to improve these respects.
For example, it has been described in Japanese Patent Application Laid-Open No. 2003-229242 that an apparatus (fixing apparatus) for heating a heating object member by the induction heating has an optical system and a mirror for guiding infrared rays radiated from a heating object member to infrared-ray detection means, and power supplied to heating means for heating the heating object member is controlled based on the detected infrared rays.
For example, it has been described in Japanese Patent Application Laid-Open No. 2003-57987 that in a fixing apparatus comprising a temperature detection device which detects the infrared rays emitted from a fixing roller to thereby speculate and detect the temperature of the fixing roller, infrared-ray emission of the fixing roller in a wavelength region detectable by the temperature detection device is set to be not more than the infrared-ray emission of the toner in the wavelength region, and an infrared-ray detection member has a film member which absorbs the infrared rays.
For example, it has been proposed in Japanese Patent Application Laid-Open No. 2003-57989 that in an apparatus for controlling a surface temperature of a heating/fixing rotary member for a fixing apparatus, comprising: a temperature detection device; and contact state switching means capable of switching a contact state between the temperature detection device and the heating/fixing rotary member, the contact state and non-contact state of surface temperature detection means be switched.
However, the proposal of any of the above-described documents relates to contact temperature detection means. Response of the contact temperature detection means differs from that of a non-contact temperature sensor. Therefore, detected temperature includes a time lag. Therefore, it is difficult to correctly manage fixing temperature of the heat roller. A sliding surface of a detection surface of the contact temperature detection means is deteriorated with life of the heat roller (increase of the number of image formed/fixed sheets). Therefore, the response of the sensor accompanying deterioration of radiation of the infrared rays is deteriorated, and a detected temperature becomes incorrect (wrong detection). As to the infrared-ray radiation, the deterioration differs depending on individual places on the surface of the roller. Therefore, when correction coefficient is equal, the detected temperature includes an error.